GNURadio -- Beginner's questions

[Swamp Thing]

I would like to experiment with GNURadio (https://www.gnuradio.org/) to process the audio that I can hear from online radio receivers (with web interfaces) like WebSDR and KiwiSDR. I have a couple of questions.

General question: I have installed GNURadio on my Raspberry Pi 5. Would it be fast enough to process audio frequency inputs in real time to decode digital modulation with bandwidths of 1 or 2 khz?

Specific Question: I want to pipe the output that I can hear on the receiver's web page, to an "Audio Source" block in GNURadio. I have tried following these instructions:
1) https://stackoverflow.com/questions/32213443/gnu-radio-use-sound-output-as-input-source
2) https://wiki.archlinux.org/title/PulseAudio/Examples#ALSA_monitor_source

I can now see "Monitor of Bluetooth Headphones" in the PulseAudio volume control, and I can see it listed as a monitor when I run pactl list. I have entered its name (which is bluez_output.A2_10_10_A1_3A_5F.1.monitor) into the "Name" field in the Audio Source Block. However, the block's output pin and the connection wire are shown in red (which I understand indicates an error). The "Run" button is greyed out.

How can I fix this problem with the Audio Source?

====== UPDATE ======

I just found that there is a red "x" button that opens an error window. The error was that I was trying to wire a "float" type source into a "complex" block. After inserting a float-to-complex converter, I can now run the flow. But I have a new issue:

QStandardPaths: XDG_RUNTIME_DIR not set, defaulting to '/tmp/runtime-root'
ALSA lib pcm.c:2666:(snd_pcm_open_noupdate) Unknown PCM bluez_output.A2_10_10_A1_3A_5F.1.monitor
audio_alsa_source :error: [bluez_output.A2_10_10_A1_3A_5F.1.monitor]: No such file or directory

==== UPDATE - 2 ====
Problem solved: You have to put in the monitor source's alias name that you create in asound.conf, as per the two links in my question. Silly me, I put in the internal system name rather than the alias of the monitor source.